Lipids

Learning Objectives: What is lipid? What is the importance of lipid in human physiology/human biochemistry? Types of lipids found in the human body. What are HDL and LDL? Outline the difference between HDL and LDL cholesterol and outline its importance.

What is lipid? Lipids are organic molecules with long hydrocarbon chains that are soluble in non- polar organic solvents. They are generally divided into three classes: – Triglycerides – Fats and Oils – Phospholipids – Lecithin – Steroids - Cholesterol

1-Triglycerides--Fats and Oils Fats and oils are triesters formed from the condensation reaction of glycerol (1,2,3, propanetriol) with long chain fatty acids. Fig page 504

Fats and Oils Fats are generally solids at room temperature, while oils are usually liquids. Fats contain saturated hydrocarbon chains. Fig page 505 Oils contains unsaturated hydrocarbon chains, with at least 1 C=C. They are known as polyunsaturated. Fig page 505

Unsaturated Fatty acids The presence of the C=C in the unsaturated fatty acid chain changes the bond angle from about C to around 120 o C. – Fig 13.16&13.17 page 505. This kink in the carbon chain keeps the fatty acids from packing as closely together.

Differences in melting points The carbon atoms in the hydrocarbon chain form a succession of tetrahedrons. This arrangement of carbon atoms makes packing of parallel chains of fatty acids fairly closely together. Forces of weak van der Waals attractions maintain the attractions between the hydrocarbon chains.

The van der Waals forces are weaker in unsaturated fatty acids and therefore require less energy to separate them

Fatty Acids Stearic acid and linoleic acid have the same number of carbon atoms but very different melting points. Stearic acid:CH3(CH2)16COOH m.p O C Linoleic acid: (omega-6-fatty acid) m.p.=-5.0 O C Linolenic acid: (omega-3-fatty acid) – page 506 – Table 22 of IB data booklet.

Assignment Find the common formula and source of following saturated and unsaturated fatty acids: – Lauric acid – Palmitic acid – Stearic acid – Arachidic acid – Oleic acid – Linoleic acid

Saturated and unsaturated fats and nutrition Most animal fats are saturated fats. They are usually solids at room temperature. Vegetable oils are more unsaturated. They liquids at room temperature. 5 FOODS TO NEVER EAT oduction.html oduction.html

Fats and oils Unsaturated (C=C) oils can be hydrogenated to form solid, saturated fats by the reaction with hydrogen gas in the presence of nickel or platinum as a catalyst. – Health issues related to hydrogenated vegetable oils –– – – o o –

Essential fatty acids Certain fatty acids must be obtained in the diet and are therefore known as essential fatty acids. They are mainly obtained from plant and fish sources e.g These fatty acids are involved in many metabolic process including synthesis of lipds called prostaglandins (lowering blood pressure)

Certain fatty acids especially omega-3-fatty acids control LDL level or lower LDL cholestrol and prevent heart disease.

Linolenic acid-(cis,cis,cis-9,12,15- octadecatrienoic acid) It is omega-3-fatty acid, essential fatty acid. It is cis isomer. The omega indicate C=C bond from the end of the CH 3. – Page no 506

Linoleic acid-(trans,trans-9,12- octadecadienoic acid) When fatty acids are made synthetically by partially hydrogenating other polyunsaturated fatty acids, some trans isomers may be formed. They are mainly found with fried foods and in some margarines. – Page 506 They are consider to increase the formation of LDL cholesterol.

The Iodine Index The degree of unsaturation can be measured by measuring the amount of iodine that can react with the unsaturated fat or oil. Each mole of C=C requires one mole of I 2 to react. Page 506

The haloalkane chain is nearly colorless. Therefore unsaturated hydrocarbon chains will destroy purple brown color of iodine solutions as long as there are C=C bonds present. Worked example: Determine iodine number page 506

Assignment--Find iodine index Butter fat Beef tallow Olive oil Peanut oil Canola oil Sunflower oil

Metabolism of fat Fats provide more energy than carbohydrates. They require greater degree of oxidation to become CO2 and H2O. The number of oxygen molecules needed to oxidize a fat is greater than for carbohydrates and it takes longer time to oxidize fats. They only digestion or hydrolysis in the presence of lipases form fatty acid and glycerol. Read digestion of fats—page 508

2-Phospholipids A phospholipid are similar to triglycerides in that they are also derived from fatty acids and glycerol, but have only two fatty acids condensed onto the glycerol molecule. The third –OH position of the glycerol has phosphate group. – Fig page 508

Different phospholipids differ in their fatty acid chains and in the group attached to the phosphate Phospholipids have a polar or hydrophilic head (phosphate group) and two non polar or hydrophobic tails (hydrocarbon chains of the fatty acids).

Phospholipids are present with cell membrane of plant and animal cell. The cell membrane must protect the cell from the intercelluar fluids around it. At the same time it must allow cell nutrients to enter the cell and waste products to leave. In PM they are present as bilayer. – Fig page 508

Steroids Steroids are hydrophobic (mostly non-polar) molecules, bearing a common structure, known as the steroid backbone. This is made up of three six-membered rings (called A, B and C) and a five-membered ring (called D) fused together. The steroids vary depending on the type and position of substituents on the steroid backbone. There is also usually a carbon–carbon double bond in either ring A or ring B. Oestrogens are different to the other steroids, in that they have an aromatic

Cholesterol (Figure B22) is a major steroid found in the body. It is found in cell membranes, where it maintains fluidity of the membrane, and it is also the precursor of other steroids, such as those mentioned above, as well as bile acids and vitamin D. Although cholesterol plays an important role in the body, it can also have a negative effect on health, in that it can contribute to heart disease.

3-Cholestrol Cholesterol has characteristic four ring structure that is common to all steroids. OR Cholesterol is one of the most important steroid. – Page 509 Cholesterol exists in esterified form in fatty acids and in a free form. Cholesterol is synthesized by liver, or available through food.

Cholesterol is component of all tissues and is found in the blood, brain and the spinal cord. Cholesterol is the steroid used in synthesis of many other bodily steroid including sex hormones and adrenocorticoid hormones (ADH) as well in the synthesis of vit D.

Role-1-Hormone Manufacturing One of the most important jobs of cholesterol is to aide in the production of hormones. Cholesterol is stored in the adrenal glands, ovaries and the testes and is converted to steroid hormones. These steroid hormones perform other vital duties to help the body function properly. According to 3DChem.com, without steroid hormones we will have malfunctions with weight, sex, digestion, bone health and mental status. body/#ixzz1aEseIQhP body/#ixzz1aEseIQhP

Role-2-Digestion Cholesterol plays an important role in our body's digestion. Cholesterol is used to help the liver create bile which aids us in digesting the food that we eat. Without the bile our bodies are unable to properly digest foods, especially fats. When the fat goes undigested it can get into the bloodstream and cause additional problems such as blockages of the arteries and cause heart attacks and heart disease. cholesterol-body/#ixzz1aEtG2Z1z

Role-3-Building Blocks Cholesterol is a structural component of cells. Cholesterol along with polar lipids make up the structure of each and every cell in our bodies. Cholesterol is there to basically provide a protective barrier. When the amount of cholesterol increases or decreases, the cells are affected. This change can affect our ability to metabolize and produce energy. This can ultimately affect other aspects of our bodies' function such as food intake and digestion. cholesterol-body/#ixzz1aEtTx7oy

Cholesterol is transported around the body by lipoproteins (LDL-low density lipoproteins). LDL transport cholesterol to the arteries where it can build up and cause cardiovascular disease. LDL result from saturated fats, especially lauric, myristic and palmitic acids.

High density lipoproteins (HDL) are smaller chain hydrocarbons. HDL can remove cholesterol from the arteries and transport it back to the liver.

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